The present invention relates to steel piles used for foundation of buildings and others. More particularly, the present invention relates to screwed steel piles-having blades for digging and also relates to a method of construction management therefor.
In the pile driving method or the pile displacing method, which is a conventional construction method for foundation piles used for construction of buildings and others, problems may be caused by noise and vibration generated in the process of construction. In order to solve the above problems, screwed steel piles have already been proposed. For example, Japanese Examined Patent Publication No. 2-62648 discloses a screwed steel pile characterized in that: an opening of a forward end portion of a steel pile body is closed by a bottom plate; a excavation blade is provided on the bottom plate so as to reduce a penetrative resistance of the pile; and a spiral wing is provided on an outer face of a lower end portion of the pile body. This screwed pile is buried in the soil in such a manner that soil and sand located at the forward end of the pile body is weakened by the excavation blade provided at the forward end of the pile body, and the pile is screwed into soil and sand, which has not been drilled yet, so that the wing can drill into the soil and sand.
However, the following problems may be encountered in the above screwed steel pile. The wing is arranged at an upper position of the bottom plate on the side of the pile body, and further the excavation blade and the wing are uncontinuously arranged with each other. Therefore, it is difficult for soil and sand, which is located at a position lower than the bottom plate, to be moved upward in the process of construction. Accordingly, it becomes difficult to generate a sufficiently high intensity of thrust. Especially when the soil at the bottom plate portion is hard and the soil close to the wing is soft, it very difficult for soil and sand to be moved to an upper portion of the wing.
In order to enhance the excavation effect, it is effective to provide a large size of blade on the bottom plate. However, the following problems may be encountered according to this structure. Although the efficiency of excavation can be enhanced, even if drilling of the pile is finished, the ground at the forward end of the pile is softened. Therefore, it is impossible to obtain an effectively high intensity of bearing capacity.
In order to solve the above problems, the following method is proposed. For example, according to Japanese Unexamined Patent Publication No. 8-226124, in the case of a steel pipe pile having a screw wing at the forward end, there are provided opening ribs for blocking soil and sand during penetrating the steel pipe pile, which are arranged inside the steel pipe pile at an upper position of the forward end of the steel pipe. That is, no conventional bottom plate is arranged at the lower end of the steel pipe pile. Accordingly, a penetrative resistance is low, and it is possible to penetrate the steel pipe pile by torque of low intensity. However, even if the above steel pipe pile is used, it is impossible to enhance the construction accuracy of the steel pipe pile. The reason why it is impossible to enhance the construction accuracy the steel pipe pile is that configurations of the spiral wing and the forward end portion of the steel pipe are not appropriate. Further, Japanese Unexamined Patent Publication No. 8-291518 discloses a steel pipe pile in which a plurality of rows of spiral wings are provided at a forward end of the outer circumferential portion of the steel pipe pile, and the interval, length and height of the spiral wing are specified, and further an incomplete wing is arranged at the lower end of the steel pipe pile. In this steel pipe pile, since this incomplete wing is attached to the side of the steel pipe, a projected area of the wing exceeds 360xc2x0, and the construction efficiency is deteriorated.
Japanese Unexamined Patent Publication No. 8-326053 discloses a steel pipe pile in which a forward end portion of the pipe pile body is spirally cut out along the outer circumference, and a spiral bottom plate, which is used as an excavation cutter, the diameter of which is approximately twice as large as that of the pile body, is fixed to a forward end face which has been cut out.
When this steel pipe pile is used, it is possible for the spiral bottom plate, which is also used as an excavation blade, to facilitate drilling and softening soil and sand at the forward end portion of the pile body, and even in the case of a pile body, the diameter of which is large, it can be easily rotated and advanced into the ground. However, essentially, the above steel pipe pile is a pile, the forward end portion of which is closed by the bottom plate. Therefore, in the process of construction, this steel pipe pile is given a high intensity of reaction force by the ground located in a portion close to the bottom plate.
For the purpose of reducing the penetrative resistance given to the forward end of the pipe so that the drilling torque can be reduced in the process of construction, the present inventors have already proposed a pile, the forward end of which is open, in Japanese Patent Application No. 9-314461. The present invention is accomplished as a variation of the above patent application. According to the present invention, the excavation efficiency can be remarkably enhanced, that is, the drilling torque can be remarkably reduced and the penetration efficiency of can be remarkably enhanced.
As shown in FIG. 23, according to the method of construction of this screwed steel pile, the screwed pile 1 includes a spiral wing 2, which will be referred to as a wing hereinafter in this specification, arranged at a lower end portion of the pile 1, wherein soil and sand is pushed in the direction of the side of the pile by the wing so that the pile can be given thrust.
In this connection, usually, a large number of piles are excavated into the ground. Therefore, in order to shorten the work period of pilling, it is important to enhance the efficiency of excavation of one pile.
According to the prior art described before, in the case where the strength of the ground 100 changes suddenly, the resistance given to the bottom plate 4 arranged at the lower end of the pile 1 exceeds a force of thrust generated by the wing. In this case, an amount of penetration of the pile is approximately not more than 5 mm. Therefore, a gap is formed under the lower face of the wing. When the above state continues, the wing is idly rotated, that is, it becomes impossible for the pile to generate a force of thrust. The aforementioned prior art has the above disadvantages.
In order to solve the above problem of the prior art in which it becomes impossible for the pile to generate a force of thrust, force F is given to the pile top as shown in FIG. 23 so that the ground close to the bottom plate can be scraped off a little. In this way, the pile is rotated until a predetermined intensity of thrust can be obtained. When a capacity of a pile driver used for burying the pile is insufficient, it becomes necessary to replace the pile driver with another pile driver having a large capacity.
As described above, when the prior art is used for constructing the piles, it takes a long time, which causes a large loss.
A configuration of the excavation blade attached to the bottom plate portion has been improved, and also a configuration of the forward end portion of the wing has been improved. However, these configurations are determined according to the nature of the ground to be excavated so that the ground can be excavated effectively. Therefore, when the nature of the ground is changed, the excavated efficiency is greatly deteriorated. That is, it is difficult to replace the wing and the pile with the most appropriate ones according to the nature of the ground 100.
In this connection, in order to build buildings and others stably on the ground, it is necessary that a bearing capacity, the intensity of which is the same as that of the designed value, is provided by the foundation pile. Since the circumstances of the pile and the ground cannot be measured and checked by a builder who is on the ground, it is desirable that the bearing capacity of the pile is estimated by the construction record.
However, except for the driven pile, the bearing capacity of which can be estimated by an penetrative resistance obtained in the process of construction, the bearing capacity cannot be estimated by the construction record. In the case of a bored pile or a cast-in-place-pile, it is impossible to estimate the bearing capacity of the pile by the circumstances of construction.
In the conventional screwed pile, drilling torque is used for the confirmation of the bearing stratum of the ground in the construction management. It is commonly said that drilling torque is appropriate to grasp the circumstances of the ground. However, drilling torque fluctuates greatly. Therefore, when the construction management is conducted only according to the drilling torque, there is a great risk of misjudging the circumstances of the ground.
Conventionally, the following specific construction methods are provided. The prior art is described as follows. In one method, the screwed pile in which a pile, the end of which is open, is screwed and given a load at the same time, so that the pile can penetrate into the ground. In the other method the inside-drilling method in which an auger rod is rotated inside a pipe pile to be displaced into the ground, so that the ground can be excavated and the pipe pile can intrude into the ground.
In the case of the method described in the above prior art, only rotation and load are given to the pile. Therefore, it is possible to conduct the excavation of a pile in the soft ground. However, according to the above screwed pile method, soil and sand rises in the pipe pile. Accordingly, soil and sand blocks the pipe pile when it rises to a certain position in the pipe pile. As a result, a penetrative resistance is increased and the excavation rate is decreased. When the pile penetrates a hard intermediate bearing stratum or the pile is put into a hard bearing stratum and when a diameter of the pipe pile is large, the motor capacity is not sufficient, so that the pile cannot penetrate the ground. Therefore, the excavation efficiency is lowered. In order to solve the above problems, it is necessary to increase the capacity of the construction machine.
In the inside-drilling method, the auger rod is rotated and the pile is displaced into the ground. According to the above method, waste soil and sand is raised by the auger rod, and a soft ground around the pile can seldom be tightened. Therefore, it is difficult to obtain a sufficiently high bearing capacity of the pile. According to this method, it is necessary to excavate the ground in the pipe pile at all times. Therefore, unless a circumferential face fixing solution is used, the circumferential face friction is reduced.
A first object of the present invention aims at an open end screwed steel pile, the forward end of the pile body of which is open, or a closed end screwed steel pile, the entire forward end of the pile body of which is closed by a bottom plate. It is a first object of the present invention to provide a screwed steel pile characterized in that: when the ground strength is suddenly increased, the pile can easily penetrate into the ground; and a high intensity of bearing capacity can be finally provided.
It is a second object of the present invention to provide a method of construction management of a screwed steel pile characterized in that: a bearing capacity can be easily estimated by the construction record, so that a foundation, the bearing capacity of which is more than that of a designed value, can be positively provided. Also, it is a second object of the present invention to provide a screwed steel pile characterized in that: drilled soil and sand located in a lower position of the bottom plate of the screwed pile is easily moved to an upper position of the wing, so that the penetration performance is high and the construction efficiency is enhanced.
It is a third object of the present invention to provide a method of construction of a screwed steel pile characterized in that: when the screwed steel pile is idly rotated, the problem of idle rotation of the screwed steel pile is quickly solved, so that the penetration efficiency can be enhanced and penetrate into the ground can be facilitated.
It is a fourth object of the present invention to provide a method of construction of a screwed steel pile and a device of penetrating a pipe pile characterized in that: in the case of a soft ground, soil and sand is forcibly discharged outside the pipe pile, so that the ground can be consolidated and tightened; and in the case of a hard ground, excavating can be conducted in a short period of time.
The summary of the invention will be described as follows.
The first present invention provides a screwed steel pile, the main body 1 of which is composed of a hollow pipe, a forward end of the main pile body 1 being open or closed by a bottom plate arranged on the entire face of the forward end portion, one or a plurality of wings 2 being arranged on the outside 1a of the forward end portion of the main pile body 1, and a forward end portion 2a of the wing 2 protruding downward from a face 1b of the forward end of the main pile body 1. In the case where a plurality of wings are provided, the lowermost wing 2 is protruded downward from a face 1b of the forward end of the main pile body 1.
The second present invention provides a screwed steel pile according to claim 1, wherein the forward end portion 2a of the wing 2 is extended in the radial direction so that it can protrude from an inside face 1c of the main pile body 1.
The third present invention provides a screwed steel pile according to claim 1 or 2, wherein the wing 2 is made of an abrasion resistance steel plate or a low friction steel plate.
The fourth present invention provides a screwed steel pile according to one of claims 1 to 3, wherein a excavating blade 3 is attached to a forward end portion 2a of the wing 2. In the case where a plurality of wings are provided, a excavating blade 3 is attached to a forward end portion 2a of the lowermost wing 2.
The fifth present invention provides a screwed steel pile according to one of claims 1 to 4, wherein the width of the wing 2 is changed in the circumferential direction so that the width of the forward end portion 2a can be narrowest and the width of the upper portion 2b can be widest.
The sixth present invention provides a screwed steel pile according to one of claims 1 to 5, wherein the thickness of the wing 2 is changed in the radial direction so that the inner circumferential portion 2c joined to the outside la of the pile body 1 becomes thickest and the outer circumferential portion 2d becomes thinnest.
The seventh present invention provides a screwed steel pile according to one of claims 1 to 6, wherein an end portion of the main pile body 1 located downward with respect to the wing 2 (the lowermost wing in the case of a plurality of wings) is cut off along the wing 2.
The eighth present invention provides a screwed steel pile, the main body 1 of which is composed of a hollow pipe, a forward end of the main pile body 1 being open, alternatively a forward end of the main pile body 1 being closed by a bottom plate arranged all over the forward end of the main pile body 1, one or a plurality of wings 2 being arranged on the outside 1a of the forward end portion of the main pile body 1 or on the forward end face 1b of the main pile body 1, and a portion 2c on the inner circumferential side of the wing 2 arranged on the forward end face 1b protruding from the inside 1c of the main pile body 1.
The ninth present invention provides a screwed steel pile, the forward end portion of the main pile body of which is provided with a bottom plate ring so that the screwed steel pile is formed into an open end pile, or the forward end portion of the main pile body of which is provided with a bottom plate so that the screwed steel pile is formed into a closed end pile, one or a plurality of wings being arranged on the outside of the lower end portion of the pile, the lower end portion of the wing being protruded downward with respect to the bottom plate ring or the bottom plate, and the protruding portion being extended in the radial direction of the pile so that the protruding portion can reach the bottom plate ring or a portion of the bottom plate or the entire bottom plate, wherein the extending portion and the protruding portion are formed into a excavation blade.
The tenth present invention provides a screwed steel pile according to claim 9, wherein the inside of the bottom plate ring is protruded from the inside face of the main pile body, and a soil and sand blocking effect generating ring is provided on the inside face of the main pile body in an upper portion of the bottom plate ring.
The eleventh present invention provides a method of construction management for managing the excavation of a screwed steel pile having one or a plurality of wings on the outside of the lower end portion of the pile, comprising the steps of: finding penetration resistance during excavation; and controlling to continue and/or complete penetration of the screwed pile according to the penetration resistance while the penetration resistance is being found.
The twelfth present invention provides a method of construction management for managing the penetration of a screwed steel pile, wherein penetration resistance Rp is found by the following equation.
Rp={(cos xcex8xe2x88x92xcex1 sin xcex8)(Htxe2x88x92Qwh)+(sin xcex8+xcex1 cos xcex8)Lb}/{(1+xcex3)(sin xcex8+xcex1 cos xcex8)+xcex1(Dpxe2x80x2/Dwxe2x80x2)(cos xcex8xe2x88x92xcex1 sin xcex8)}
xcex8: Angle of a wing with respect to a face perpendicular to a pile axis
xcex1: Coefficient of friction between a ground and a steel plate
Ht: Value obtained when torque acting on a pile end is converted into a horizontal force on an action circle
Lb: Upper load acting on a pile end
Dpxe2x80x2: Diameter of an action circle of a bottom plate
Dwxe2x80x2: Diameter of an action circle of a wing
Qwh: Horizontal resistance of a ground received by a cutter end
xcex3: Coefficient of resistance of a perpendicular cutter end
Rp: Penetration resistance of a ground received by a bottom plate portion which is a projected area portion of a bottom plate ring or a bottom plate.
The thirteenth present invention provides a method of construction management for managing the penetration of a screwed steel pile, wherein bearing capacity Qu of a pile end is estimated by the following equation.
Qu=(Rp/d)xc3x97{1+e(Aw/Ap)}
where Aw is a projected area of a wing, Ap is a projected area of a bottom plate portion, e (0 less than exe2x89xa61) is an effective working ratio of a wing portion, d is a coefficient of correction determined by a quantity of penetration at the time when a pile penetration is finished, and Qu is a bearing capacity of a pile end.
The fourteenth present invention provides a method of construction management for managing the penetration of a screwed steel pile, wherein pulling capacity Qup of a pile end with respect to pulling is estimated by the following expression.
Qupxe2x89xa7Rpxe2x88x92Lb
where Qup is a pulling capacity of a pile end with respect to pulling.
The fifteenth present invention provides a method of construction management for managing the construction of a screwed steel pile having one or a plurality of wings on the outside of the lower end portion of the pile, comprising the steps of: finding penetration resistance Rp by the following equation in the process of penetration; and controlling to continue and/or complete penetration of the screwed steel pile according to the penetration resistance while the penetration resistance is being found.
Rp=[2xcfx80Tb+Lb{(1xe2x88x92c)S+cP+xcex1xcfx80Dwxe2x80x2}xe2x88x92Qwhxcfx80Dwxe2x80x2xe2x88x92QwvS]/{(1xe2x88x92c)S+cP+xcex1xcfx80(Dpxe2x80x2+Dwxe2x80x2)}
xcex1: Coefficient of friction between a ground and a steel plate
Tb: Torque acting on a pile end
Lb: Upper load acting on a pile end
P: Wing pitch
S: Quantity of penetration per one revolution
Dpxe2x80x2: Diameter of an action circle of a bottom plate or a bottom plate portion
Dwxe2x80x2: Diameter of an action circle of a wing
Qwh: Horizontal resistance of a ground received by a cutter end
Qwv: Vertical resistance of a ground received by a cutter end
c: Coefficient of consumed energy by a ground caused by forced deformation of a wing directed upward
Rp: Penetration resistance of a ground received by a bottom plate of a bottom plate portion which is a projected area portion of the bottom plate.
The sixteenth present invention provides a method of construction management for managing the construction of a screwed steel, wherein bearing capacity Qu of a pile end is estimated by the following equation.
Qu=(Rp/d)xc3x97{1+e(Aw/Ap)}
where Aw is a projected area of a wing, Ap is a projected area of a bottom plate or a bottom plate portion, e (0 less than exe2x89xa61) is an effective working ratio of a wing, d is a coefficient of correction determined by a quantity of penetration at the time when the penetrating of a pile is finished, and Qu is a bearing capacity of a pile end.
The seventeenth present invention provides a method of construction management for managing the construction of a screwed steel pile, wherein pulling capacity Qup of a pile end with respect to pulling is estimated by the following expression.
Qupxe2x89xa7Rpxe2x88x92Lb
where Qup is a pulling capacity of a pile end with respect to pulling.
The eighteenth present invention provides a method of construction of a screwed steel pile comprising the steps of: rotating a screwed steel pile having a wing at the forward end portion so as to penetrate the screwed steel pile into the ground; reversing the screwed steel pile so as to draw it by an appropriate distance when a quantity of penetration of the a screwed steel pile is remarkably decreased; and rotating the screwed steel pile again so as to penetrate it into the ground.
The nineteenth present invention provides a method of construction of a screwed steel pile comprising the steps of: rotating a screwed steel pile having a wing at the forward end portion so as to penetrate the screwed steel pile into the ground; reversing the screwed steel pile so as to draw it by a distance at least not less than a pitch of the wing when a quantity of penetration of the screwed steel pile is remarkably decreased; and rotating the screwed steel pile again so as to penetrate it into the ground under the condition that a pile head is given a load directed downward.
The twentieth present invention provides a method of construction of a screwed steel pile, in which the inside-drilling method is also used, comprising the steps of: drilling, rotating and penetrating the screwed steel pile on a soft layer of a ground and discharging drilled soil and sand to a periphery of the pile so that the drilled soil and sand cannot enter the pile; and conducting inside-drilling on a hard intermediate stratum or a support stratum so that the drilled soil and sand can enter the pile.
The twenty first present invention provides a method of construction of a screwed steel pile described above, wherein drilled soil and sand is made to enter the screwed steel pile by the inside-drilling method when the screwed steel pile is penetrated into a support stratum, and solidification material such as cement mortar or cement milk is jetted out from an end of the auger so that the jetted solidification material is solidified and integrated with the forward end portion of the screwed steel pile, and the screwed steel pile is supported by and fixed to the support stratum of the ground.
The twenty second present invention provides a method of construction of a screwed steel pile comprising the steps of: inserting an auger used for inside-drilling having a spiral wing of an appropriate length into the screwed steel pile, the end of which is open having a drilling wing outside of the forward end of the screwed steel pile body, from the lower side, the rotation of the auger being controlled separately from the rotation of the pile; rotating and penetrating the pile into a soft stratum of the ground so as to drill soil and sand by the drilling wing and forcibly discharge the drilled soil and sand to the periphery of the pile body, the rotation of the auger being stopped during penetrating the pile so that soil and sand cannot enter the pile; and drilling and rotating the auger on a hard stratum of the ground such as an intermediate stratum and a support stratum of the ground so that the drilled soil and sand can enter the pile.
The twenty third present invention provides a method of construction of a screwed steel pile comprising the steps of: using a screwed steel pile, the end portion of which is open, having a drilling wing for drilling a ground, arranged outside in a lower portion of the pile, also using an auger having a spiral wing for drilling of an appropriate length, mounted on an auger shaft inserted into the pile, also using a pipe pile drive section for rotating the pile, and also using an auger drive section for rotating the auger in the normal and the reverse direction; drilling, rotating and penetrating the pile into a soft stratum of the ground so as to drill soil and sand by the drilling wing and forcibly discharge the drilled soil and sand to the periphery of the pile body, the rotation of the auger being stopped during penetrating the pile so that soil and sand cannot enter the pile; drilling and rotating the auger on a hard stratum of the ground such as an intermediate stratum and a support stratum of the ground so that the drilled soil and sand can enter the pile; and drawing out the auger from the pile after the completion of penetration of the pipe pile.